Protein crystals have shown significant benefits in the delivery of bioactives to achieve high concentration, low viscosity, extended release profiles, and improved stability. Li et al, Acta Cryst., F63:599-601 (2007); Basu et al, Expert Opin. Biol. Ther., 4(3):301-317 (2004); Yang et al, PNAS, 100(12):6934-6939 (2003). Some proteins and peptides have been crystallized alone or co-crystallized with zinc in an attempt to make extended release products. Y receptor agonists, complex compounds that often possess inadequate stability and short half-life, have limited delivery options. There is a need in the art for formulations of Y receptor agonists that have extended release properties and that have suitable stability. The disclosure is directed to these, as well as other, important ends.